Bulk cargo hoppers that store and dispense bulk cargo are well known. The typical bulk cargo hopper employs vacuum pressure to draw bulk cargo to the hopper and into an interior volume of the hopper. The bulk cargo drawn to the hopper is temporarily stored in the hopper. When it is desired to dispense the stored bulk cargo from the hopper, the vacuum pressure supplied to the hopper is stopped and an outlet valve at the bottom of the hopper is opened. This allows a desired amount of the stored bulk cargo to fall from the interior volume of the hopper and into a container positioned below the outlet valve. When the container is filled with the dispensed bulk cargo to a desired amount, the outlet valve is closed. The container is then moved from beneath the hopper, allowing a further container to be positioned below the outlet valve of the hopper and filled with a desired amount of the bulk cargo from the hopper by opening the outlet valve.
Hoppers of the type described above are employed in the production of plastic material in the form of pellets, granules, powders, etc. that are later used in plastic extrusion manufacturing processes. The plastic material, for example small plastic pellets of a single color are drawn into the interior volume of the hopper by the vacuum pressure in the interior of the hopper supplied by a vacuum pressure source.
When it is desired to fill a container with the colored pellets, the vacuum pressure supplied to the hopper is stopped and the outlet valve of the hopper is opened. This allows a desired amount of colored pellets in the hopper to fall into the container.
A disadvantage of this product transferring method is that batches of the colored pellets produced and supplied to the hopper will often have slightly different colors. For example, a first batch of red pellets fed to the hopper may have a particular shade of red. A second batch of red pellets fed to the hopper and layered on top of the first batch of pellets may have a slightly different shade of red.
At some time during the unloading of the pellets from the hopper to a container, a portion of the first batch of pellets will be loaded into a container together with a portion of the second batch of pellets. The container, containing pellets of slightly different colors would then be sent to a manufacturer of plastic products. This would result in the manufacturer manufacturing plastic products having two different colors. For example, the manufacturer would manufacture a group of products having one shade of red and another group of products having a slightly different shade of red. This is an undesirable occurrence for the manufacturer that desires all of their products offered to consumers have the same color.